1. Field of the Invention
The present invention relates to a roller separating apparatus for a laser printer, and more particularly, to a roller separating apparatus for a laser printer which separates rollers from one another to prevent foreign material accumulated at the seam of a circulating photoreceptor belt from being transferred to the rollers.
2. Description of the Related Art
Referring to FIGS. 1 through 3, a conventional laser printer includes a transfer backup roller 11a, a steering roller 11b, and a driving roller 11c arranged in a triangle. A photoreceptor belt 12 forms a closed loop which circulates around the three rollers 11a, 11b, and 11c. A stepped seam portion 12a is formed on the photoreceptor belt 12 where the ends of the photoreceptor belt are joined together. A plurality of laser scanning units (LSUs) 15 and a plurality of development units 16 are installed adjacent to the photoreceptor belt 12 between the steering roller 11b and the driving roller 11c. The LSU's direct light beams onto the photoreceptor belt 12 according to input image information, thereby forming an image area. The development units 16 fix a developer onto the image area formed by the LSUs 15, thereby developing an image.
A transfer roller 17 opposes the transfer backup roller 11a, such that the photoreceptor belt 12 interposes therebetween. A fusing roller 18 opposes the transfer roller 17 to rotate in contact with the transfer roller 17. When a section of the photoreceptor belt 12 carrying the image passes between the transfer roller 17 and the transfer backup roller 11a, the transfer roller 17 lifts the image from the photoreceptor belt 12. The image transferred to the transfer roller 17 is printed on a paper 19 passing between the transfer roller 17 and the fusing roller 18.
Foreign material 1 such as dirt and used toner accumulate on the seam portion 12a of the photoreceptor belt. Such foreign material 1 adheres to the transfer backup roller 11a, the transfer roller 17, the fusing roller 18, and eventually prints on the paper 19, thereby deteriorating the print quality. Therefore, a roller separating apparatus 20 is provided to prevent the foreign material 1 from transferring to the transfer roller 17 and the fusing roller 18.
When the seam portion 12a of the photoreceptor belt 12 passes between the transfer backup roller 11a and the transfer roller 17, the roller separating apparatus 20 separates the transfer backup roller 11a, the transfer roller 17, and the fusing roller 18. Thus, the foreign material 1 accumulated on the seam portion 12a cannot transfer onto the transfer roller 17 and the fusing roller 18.
The roller separating apparatus 20 includes a first frame 30 on which the transfer backup roller 11a is installed, a second frame 40 on which the transfer roller 17 is installed, and a third frame 50 on which the fusing roller 18 is installed. A first motor 21, for rotating a first shaft 22, is installed on the first frame 30. A first rotating piece 23 is installed at both ends of the first shaft 22. A first protrusion 24 is formed at an offset position from the center of rotation of the first rotating piece 23. A ring 24a is fitted around the first protrusion 24 and freely rotates thereabout. The ring 24a is coupled to the second frame 40 by a first spring 25.
A second motor 41, for rotating a second shaft 42, is installed on the third frame 50. A second rotating piece 43 is installed at both ends of the second shaft. A second protrusion 44 is formed at an offset position from the center of rotation of the second rotating piece 43. The second protrusion 44 inserts into a hole 44a formed in the second frame 40. Also, a second spring 55 is installed between the second frame 40 and the third frame 50.
When the seam portion 12a passes between the transfer backup roller 11a and the transfer roller 17, the second motor 41 rotates the second rotating piece 43. The second protrusion 44 of the second rotating piece 43 moves downward and elevates the third frame 50. Thus, the fusing roller 18 separates from the transfer roller 17, as shown in FIG. 3. Next, the first motor 21 rotates the first rotating piece 23. The first protrusion 24 moves upward and elevates the second frame 40. Thus, as shown in FIG. 3, the transfer roller 17 separates from the transfer backup roller 11a.
While the rollers 11a, 17, and 18 are separated, the seam portion 12a of the photoreceptor belt 12 passes across the transfer backup roller 11a. The photoreceptor belt 12 does not contact the transfer roller 17. Thus, the foreign material 1 accumulated on the seam portion 12a is not transferred to the transfer roller 17.
After the seam portion 12a passes between the transfer backup roller 11a and the transfer roller 17, the first and second motors 21, 41, respectively, are driven in a reverse direction. The transfer roller 17 and the fusing roller 18 sequentially move toward the transfer backup roller 11a. Accordingly, the transfer backup roller 11a, the transfer roller 17, and the fusing roller 18 are positioned adjacent each other.
Although generally thought to be acceptable, the conventional roller separating apparatus 20 is not without shortcomings. In particular, two motors 21, 41 and their accompanying gears are required to separate the transfer roller 17 from the transfer backup roller 11a and the fusing roller 18 from the transfer roller 17, respectively. Thus, the structure of the roller separating apparatus 20 is complicated.